The present invention pertains to optical couplers, and more particularly to data transmission in optical networks using optical couplers.
Passive Optical Networks (PONs) facilitate the communication of two-way high-bandwidth data between a system head-end and various end nodes. A conventional PON generally includes a fiber-optic star or tree coupling device which connects optical paths extending from the system head-end to the remotely located end nodes. Downstream optical signals are transmitted from the system head-end over an optical distribution fiber to an outside plant node where the signal is passively split and distributed to the remotely located end nodes. The end nodes may transmit optically encoded signals upstream to the outside plant node to form a multiplexed signal on the distribution fiber for transmission to the system head-end.
For downstream transmission from a system head-end to remotely located end nodes, PONs may implement time division multiplex (TDM) techniques, wavelength division multiplex (WDM) techniques, or other techniques for partitioning data destined for individual end nodes. For upstream transmissions, where many end nodes may access the fiber media, the multiple access may be achieved by time division multiple access (TDMA), wavelength division multiple access (WDMA), code division multiple access (CDMA), or combinations thereof.
One of the most basic schemes utilizes TDM for downstream data transmissions and TDMA for upstream data transmissions and is often referred to as a power-splitting TDMA PON. Downstream data is a xe2x80x9cbroadcast and selectxe2x80x9d TDM stream of data frames. Each end node receives a broadcast copy of the downstream TDM data and selects its own specific data based on an address within the TDM stream. This TDM stream may occupy a single wavelength. For upstream data transmissions, end nodes achieve multiple access by synchronizing their upstream transmissions so that they occur in a pre-assigned interval. This synchronization helps eliminate overlap of upstream data transmissions from the splitter/combiner device after multiple data streams from end nodes are combined. The upstream data may be transmitted on a single wavelength which generally is a distinct wavelength from the downstream.
The process of arbitrating and synchronizing upstream data transmissions has conventionally treated the head-end as a master device and the end nodes as the slave devices. The slave devices request permission to transmit from the master; the master then schedules the time slots in the future and informs the slaves of the granted future time slots. For networks, such as a cable data network, where transmission speeds are 100 to 1000 times lower than an optical network, the negotiation time and propagation delay between the slaves and the master during this request/grant protocol between master and slave consumes an insignificant amount of upstream bandwidth and does not significantly impact upstream data transmissions. An insignificant number of data-bit periods elapse relative to the propagation delay and negotiation time. In an optical network, such as a gigabit fiber network, the request/grant negotiation and its propagation time consume a more significant amount of upstream data bandwidth because of the shorter bit times. This negotiation and propagation time could otherwise be used for upstream data transmissions.
Thus there is a need for improving upstream data transmission efficiency in an optical network. There is also a need for reducing request/grant negotiation and propagation time in an optical network. There is also a need for distinguishing between upstream data and upstream control signals for improved upstream data transmission efficiency in an optical network.